Caches might be cleared by many reasons besides manually resetting. For example, if you edited the URL pattern, or the system found disk space is very small. It is an internally managed function designed for loading performance optimization, not for offline usages.

If you want a persist and permanent cache for offline usage or sharing, please try the "Download Map" function which supports downloading any customized region of any customized map for any customized zoom levels/resolutions. check this: http://duweis.com/support/viewdoc.html? ... =056_dlmap